git-cgi.t: Exercise an alphanumeric, but non-ASCII, root page

git-cgi.t: Exercise an alphanumeric, but non-ASCII, root page

My previous attempt to reproduce this bug used a non-alphanumeric
ASCII character. This is not currently considered to be a valid
value for rootpage, although for a "do what I mean" approach, perhaps
we should accept it and pass it through titlepage() or linkpage().

Using Chinese characters (which are considered to match [[:alnum:]]
even though the Chinese script is not, strictly speaking, an alphabet),
as in the original bug report, reproduces the bug.

Signed-off-by: Simon McVittie <smcv@debian.org>